Synchronization system for television



Jan. 28, 1941- J. SCHUNACK ETAL SYNCHRONIZATIO N SYSTEM FOR TELEVISION Filed Aug. 9, 1938 3'Sheets-Sheet l INYVENTORS JOHANNES SCHUNACK ROLF MALY Jan. 28, SC N CK' AL SYNCHRONIZATION SYSTEM FOR "TELEVISION Filed Aug. 9, 1938 3 Sheets-Sheet 2 INVENTORS JOHANNES SCHUNACK RLF MAL FOF UDERT BY ,1 v

J. SCHUNACK HAL 2,230,092

Jan. 28, 1941.

SYNCHRONIZATION SYSTEM FOR TELEVISION 3 Sheets-Sheet 5 Filed Aug. 9, 1938 p ;J5o00-cm EL 28 2%s loKn J; K E1 INVENTORS JOHANNES SCHUNACK ROLF MFALY Patented Jan. 28, 1941 PATENT or-Pics sYNcnaoNIzArrIoN SYSTEM ron TELEVISION Johannes Schunack, Berlin-Friedenau, and ltolf Maly and Frithjof Rudert, Berlln-Zehlendorf, Germany, assignors to the firm Fernseh Aktien- Gesellschaft, Zehlendorf, near Berlin, Germany I Application August 9, 1938, Serial No. 223,910 In Germany August 9, 1937 This invention relates to systems of synchronization of television transmitters and receivers.

It is common in the art to use so-called interlaced scanning in which an image is not completely scanned in any one vertical scansion. Each partial scansionv or field occurs in the interstices between the traces of the preceding scansion or scar ions. ploy so-called odd-line interlaced scanning, in

10 which the number of lines per television frame is an odd number, while the number of fields per frame is an even number, and whereby the number of lines in eachfield is a non-integral multiple of the number of fields per frame.

5' In such systems it is of utmost importance to maintain the vertical scanning in a predetermined fixed relationship to the horizontal scanning in respect to time. Deviations from this fixed relation cause the scanning lines of suc- 20 cessive partial scansions not to be equidistant, but to pair off, and in extreme cases to overlap completely, whereby, in the latter case, interlace is lost altogether and the vertical resolution of the image is reduced to one-half. A continuous 25 shift in the time relation between vertical and horizontal scanning results in a motion of the fields with respect to each other, the so-called line weaving which results in an unsteady image.

30. It is customary in the art to employ separate scanning wave generators at the transmitter and receiver, and to synchronize both by transmission of two types of synchronizing impulses, e. g.,

one for vertical scanning and-one for horizontal 35 scanning. Thus, it is the accuracy of these impulses upon which perfect interlace depends. In a television system with 441 lines per fullframe, 30 full frames per second andan interlace ratio 40 in the occurrence ofthe synchronizing impulses for vertical scanning, ccmm'only referred to as the framing impulse, will cause total loss of in-- terlace.

It is known in the art, among other-methods,

45 to derive the framing impulse from the line synchronizing frequency, or from a multiple thereof, by frequency division. The leading edge of the framing impulse will, therefore, always be in a fixed relationship to the-line synchronizing im- 50 pulses. It is also known to use signals, consisting of a preparatory section and'a framing section proper, in order to obtain congruent framingimpulses for .alternate frames when using integrating networks, as is well known to those skilled in the art. In this case, the beginning of the It is also known to em-v preparatory. section of the impulse is in fixed relationship to the line synchronizing impulses; ac-

tual timing of the vertical scanning generator,

however, occurs at the end of the preparatory section, i. e'., at the beginning of the framing sec- 5 tion proper of the impulse. This necessitates high accuracy and uniformity in the duration of the preparatory signahE-btherwise, the timing of the .vertical scanning generator is subject tophase shift. However, rather great dimculties are encountered in generating preparatory signals of perfectly uniform duration.

It is the object of this invention to overcome the above-mentioned difliculties, and to provide a new method of framing impulse generation;

furthermore, to provide new means for such generation.

Broadly considered, this invention is adapted to generate a framing impulse proper, directly derived from the linesynchronizing frequency and in perfect synchronism therewith; to synchronize the generation of an impulse of longer duration than the framing impulse'proper with the latter impulse, whereby the leading edge of the longer impulse precedes that of the framing im pulse proper; to superimpose'both impulses and thereby obtain a frame impulse comprising a preparatory section and a framing impulse proper, whereby the leading edge of the framing impulse proper is in perfect synchronism with the line synchronizing frequency, and to utilize the re sultant impulses for synchronization;

In the accompanying drawings:

Figs. la, 1b, 2a, 2b, 2c, 2d, 40, 4b and 4c show" series of impulses; Fig. 3 shows, in the form of a block diagram,

a synchronizing system in accordance with the ,invention; and of 2:1, a shift of approximately 1/30,000 second Fig. 5 shows a schematic circuit diagram of one of the blocks of the system shown in Fig. 3. 40

r The invention will now be explained in detail with the aid of the drawings. Figure la illustrates the composite television signal obtained with the'prior art method; In this figure the line synchronizing impulses are indicated by the 4 numeral l, and are assumed to have aduration of 10% of the time required for scanning and retracing one line. The picture signal is indicated by the numeral 4, and the black level by numeral 5. tion of the total framing signal including the preparatory section and the framing impulse proper. The duration of the total framing signal is assumed to be 10% of the frame period, whereas the preparatory section takes up.5% thereof. 55

The interval 2 indicates the dura- It may be understood, however, that this invention is by no means limited to iraming signals of such duration and will operate Just as well on signals of considerably shorter duration. The preparatory section 6 is synchronized with the line synchronizing frequency at the time indicatwith a framing signal in accordance with the present invention. Line synchronizing impulses are indicated by numeral I. The framing signal 3 in this case may again have a duration of 10% of the frameperiod. It may be seen that the leading edge of the framing impulse proper occurs at the time indicated by the line 3 and is in absolute synchronism with the line synchronizing frequency for reasons to be explained later.

Figure 3 is a schematic diagram of a synchronizing impulse generator system according to the invention. The revolving disc possesses a series of apertures through which light from a constant source is allowed to fall, upon photocells H) and II. Photocell I! may produce picture signals in the well-known manner of the Nipkow disc. Photocell it may then produce a series of impulses of line frequency, while photocell ii may produce a series of impulses of framing frequency.- These impulses may have a duration of 5% of their respective periods. The line synchronizing' impulses are fed through a shaping network l2 in which their width is increased to 10% and in which they are given a squaretopped shape. The framing impulses are fed through a network i3, in which their width in increased to 10%, and then to a circuit is which generates the preceding signal according to the invention. Circuit I9 will be explained in detail below. The output of circuit I9 is a series of impulses of the shape shown in Figure 2b, the duration of which is approximately 10% of the frame period, and which leads the impulse produced in photocell I I by 5% of the frame period. This impulse is fed through an amplifier M and is then mixed with line synchronizing impulses. Therr'lixed impulses are then fed to a modulator stage [5, in which a carrier generated by oscillator I6 is modulated simultaneously by the mixed impulses as well as by picture signals produced by photocell l1 and amplified by amplifier IE, to produce impulses of the shape shown in Fig. 2d. The framing impulse as shown in Figore-2a, as produced by photocell I I; is amplified by amplifier and fed to a mixer stage 2|. The impulse produced by circuit IQ of the shape shown in Figure 2b is also fed to mixer stage 2 i, preferably in opposite polarity, so that the resulting impulses will have a duration and phase as shown in Figure 2c. This impulse is modulated upon the previously modulated carrier coming from modulator l5 by a modulator stage 22, so that the resultant/ Figure 5 shows a circuit which may be used to fulfill the function of circuit IQ of Figure 3. The operation of this circuit can behest explained in connection with the diagrams of Figure 4. In Figure 4a, the curve shows the series of framing impulses, wherein the line 3 modulated carrier will be oi the kind shown .in Figure lb.

indicates the leading edge of the impulse at .which the vertical scanning generator is to be synchronized. The curve of Fig. 4b shows the saw-tooth voltage output of a relaxation oscillator whosenatural-f f quency is adjusted to 'be slightly higher than that of the impulses of Fig. 4a, with which it is synchronized. Thus,

the voltage begins to rise again until, after a fraction of the natural period of .the .osclllator, a synchronizing impulse, as shown in the curve of Fig. 4a, is injected, which causes the oscillator to trip again. The saw-tooth voltage as shown by the curve of Fig. 4b is fed through a phase inverter stage and is then used to synchronize a, multivibrator upon the peaks indicated by numeral 36. The multivibrator then produces a seriesof impulses as shown by the curve of Fig. 4c which correspond to those in Figure 2b.

Figure 5 shows an embodiment of this circuit in detail. The multigrid tube '32 is in reflex oscillator connection. This circuit is self-excited and produces a saw-tooth voltage output. The frequency of the saw-tooth output can be varied by adjustment of one or both of resistors and 26. The framing impulses as shown in Figure 4a are applied to the cathode of tube 32 tube 32 the double-peaked saw-tooth voltage is applied to the control grid of another multigrid tube ,30. The bias of this tube is so adjusted that. the saw-tooth peak 36 of Fig. 4b is not cutoff. Peak 36 is then used to synchronize a multivibrator of the conventional type. as is well known in the art, which is connected at point 3!. This multivibrator then produces a series of impulses as shown in Figure 40 which correspond to those in Figure 2b. The duration of these-impulses can be varied by variation of the multivibrator circuit constants. Thus, a. series of impulses is generated, which impulses are synchronized by master impulses, whose leading edges precede those of the master impulses and whose duration isindependent of that of the master impulses.

While we have described our invention in connection with mechanical means of pict e signal and master impulse generation, it is obvious that these may readily be replaced by elec@- tronic means, as are well known in the art.

What we claim is: v 1. Method of generating synchronizing Sigrials possessing a preparatory section and a syn chronizingimpulse for television systems, comprising the steps of generating a series of mas-- said second impulses in opposite polarities, and

utilizing the resultant impulses for synchronization.

2. Method of generating synchronizing signals a preparatory section and a synchronizing impulse for television systems, comprising the steps of generating a series of master impulses at whose leading edges synchronization is to take place, applying said series of master impulses to a saw-tooth wave generator possessing a natural frequency higher than that of said series of master impulses in such polarity and phase as to generate a doublepeak'ed saw-tooth wave, utilizing the first one of said peaks to synchronize an impulse generator, generating by saidlast-named generator a second series of impulses whose leading edges in eiiect precede the leading edges of said series of master impulses and whose impulse durations are greater than those of said master impulses, superimposing said master impulses and said second impulses in opposite polarities and utilizing the. resultant impulses for synchronization.

3. The method of deriving from a first series of impulses a second series of impulses whose leading edges in eflect precede those of said first impulses, comprising the steps of applying said first impulses to a self-excited saw-tooth wave generator having a natural frequency higher than that of said first impulses in such polarity and phase as to prematurely interrupt each sawtooth cycle and thereby producing a doublepeaked saw-tooth wave, and utilizing the first one of said double peaks to synchronize an impulse generator to produce said second series of impulses.

4. The method of producing a synchronizing signal from a saw-tooth wave oscillator by appli cation thereto of a cyclic controlling pulse, which comprises tuning said oscillator to a frequency higher than the frequency of said starting pulse, applying said starting pulse to interrupt each saw-tooth cycle after start thereof, forcing the reestablishment of said cycle after stoppage, and utilizing the double-peaked output to produce said synchronizing signal, thereby effectively advancing the leading edge of said signal ahead of the leading edge of said controlling pulse.

JOH'ANNES SCHUNACK. ROLF MALY. m'mror' RUDER'I'.. 

